There have been conventionally known construction machines such as a hydraulic excavator equipped with an offset boom (see, for instance, Patent Document 1).
The offset boom includes a first boom supported on an upper rotary body and a second boom rotatably coupled to a distal end of the first boom, where the second boom can be offset relative to the first boom by a telescopic motion of an offset cylinder that connects a proximal end of the second boom to a bracket on a distal end side of the second boom.
Recently, hybrid electric rotary excavators have been being developed, in which a rotary body is driven by an electric motor and other members such as a work machine and a carrier are driven by a hydraulic actuator (see, for instance, Patent Document 2).
Since the rotation of the rotary body is driven by the electric motor in such electric rotary excavators, even when the rotary body is rotated while a boom and an arm that are driven hydraulically are lifted up, the rotation of the rotary body is not affected by the lifting of the boom and the arm. Accordingly, an energy loss at control valves or the like can be reduced as compared to an arrangement in which the rotary body is hydraulically driven, thereby enhancing energy efficiency.
[Patent Document 1]
JP-A-2002-371579
[Patent Document 2] JP-A-2001-11897